Aurora and NLC's

Displays of Noctilucent Clouds and Aurora during one night are rare.

Noctilucent Clouds, NLC's for short, (aka Night Shining Clouds or Polar Mesospheric Clouds) are the world's highest types of cloud forming on the edge of space at height of about 80 km (50 miles) which is also height where auroras occur. Unlike most of other clouds types, which are mostly made of water vapour, NLCs are comprised of extremely small ice crystals. They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. They can be observed in the summer months at latitudes between 50° and 70° north and south of the equator.
-via Maciej Winiarczyk